Conventional washing machines operate by agitating textile articles within a rotating drum in the presence of water and detergent so that dirt is released from the fibres of the textile articles into the water. The agitation is caused, in the case of front-loading washing machines, by the rotation of the drum about a generally horizontal axis so that the textile articles tumble over one another and rub against each other and against the walls of the drum. However, the rotational speed of the drum is limited because, if the speed is too high, the textile articles will merely be pressed under centrifugal forces against the interior walls of the drum. The articles then rotate with the drum and no agitation with respect to the drum or with respect to other articles is achieved. The amount of agitation which can be applied to the textile articles by front-loading washing machines is therefore limited. This means that, in order to achieve a specific standard of cleanliness, the machine must operate for a minimum period of time.
International Patent Application WO99/58753 describes a washing machine in which the drum comprises two rotatable drum portions which are driven in such a way that relative rotation is produced between the drum portions. The relative rotation between the drum portions gives a more vigorous agitation of the articles within the drum, treating them more intensively than they would be in conventional apparatus and consequently dirt is released from the textile articles at a higher rate than in other machines.